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Modulated Antenna User Manual - Prelim3
Page 6 of 10
Printed: 11/16/22
3:39 PM
LF TRANSMISSION (125KHz)
THIS MODEL ONLY GENERATES A
MODULATED LF TRANSMISSION
The JR Automation TPM Antenna systems were developed to utilize
the LF (Low Frequency) transmission to collect data from the TPM
stem. The TPM stem responds with the 125 kHz wakeup signal can
be of 2 different types – Continuous and Modulated LF. Each is
described below.
Continuous LF:
A stem requiring a continuous signal or a signal
with no change. It is simply a continuous sine wave signal at a given
frequency (125 kHz in our case). The stem will periodically “listen”
for an LF broadcast. If it hears the broadcast for a specific amount of
time (typically 1-3 seconds) the stem will respond with its UHF
broadcast. This is also commonly referred to as “non-modulated
LF”.
Modulated LF:
In this case, the LF signal is turned off and on off
quickly. This creates a pattern of pulses. Generally, a unique pattern
is generated for each stem type. The stems are designed to wake
up only if it hears a signal using its unique pattern. The antenna will
generate this unique pattern over and over until it receives the UHF
wake up response from the stem. The pulse pattern that is
generated by the antenna forms a message packet. An individual
packet is repeated over and over during the LF transmission. This
repetition of the packet gives the stem’s receiving circuits multiple
changes to receive the message, and to validate it. The pattern
within the packet is arranged into a “structure”. Typically, a packet structure consists of several fields, with each
having a specific purpose. This unique data structure is specified by the TPM Valve Stem manufacturer.
Continuous LF
Modulated LF
